The sport of running is a popular fitness activity, with an estimated 30 million Americans classified as recreational runners (Austin, 2002). The overall incidence of lower extremity injuries in runners that run ≧5 km per training day or race has been found to range between 19.4% and 79.3% (van Gent et al., 2007). The predominant joint injured is the knee (7.2% to 50.0%) followed by the ankle (3.9% to 16.6%) and hip (3.3% to 11.5%). Overuse injuries are the majority of all musculoskeletal running injuries stemming from training errors, anatomical or biomechanical factors (Hreljac et al., 2000; James et al., 1978; Macera et al., 1989).
Core stability has been defined as the lumbo-pelvic hip muscle strength and endurance yielding a coordinated activation of muscles and maintenance of alignment throughout the kinetic chain (Fredericson et al. (2005); Kibler et al. (2006); Leetun et al. (2004); Willson et al. (2005)). The stance phase of running is a closed kinetic chain activity requiring proximal stability to balance and support the weight of the upper body. When core instability exists, due to strength and/or endurance deficits, the body may not be optimally aligned to absorb and produce large ground reaction forces, which in turn could place the runner at an increased risk for lower extremity injury (Ferber et al., 2002; Marti et al., 1988). Frontal plane pelvic drop is one sign of core instability that could be identified as a weak link in the running kinetic chain. Pelvic drop in the frontal plane, termed ‘Trendelenburg gait,’ is visualized when there is a downward obliquity from the hip of the stance leg towards the opposite hip during its swing phase.
Core instability as demonstrated by frontal plane pelvic drop is due to strength and endurance issues of the gluteus medius muscle (Mann et al., 1986). The gluteus medius is one of the strongest lower extremity muscles (Ward, Eng, Smallwood, & Lieber, 2009) and is made up of three parts of nearly equal volume with three distinct muscle fiber directions and separate innervations (Dostal, Soderberg, & Andrews, 1986; Gottschalk, Kourosh, & Leveau, 1989). This muscle originates on the dorsal ilium below the iliac crest and inserts at the top outside surfaces of the greater trochanter. Based on its anatomical location, cross sectional area and architecture, the gluteus medius muscle is critical to the functions of the lower back (Nelson-Wong, Gregory, Winter, & Callaghan, 2008), hip (Bolgla & Uhl, 2005; Delp et al., 1999), knee (Boling, Bolgla, Mattacola, Uhl, & Hosey, 2006; Mascal, Landel, & Powers, 2003; Nakagawa et al., 2008) and the ankle. Hence, core instability due to gluteus medius muscle weakness will lead to abnormal spinal and lower extremity kinematics during running.
The gait adaptations due to a weak or fatigued gluteus medius muscle during running and the anatomical areas at risk of structural overload are summarized in Table 1 (Bolgla & Uhl, 2005; Boling, Bolgla, Mattacola, Uhl, & Hosey, 2006; Cichanowski et al., 2007; Fredericson et al., 2000; Ireland et al., 2003; Leetun et al., 2004; Mascal, Landel, & Powers, 2003; Nakagawa et al., 2008; Nelson-Wong, Gregory, Winter, & Callaghan, 2008; Niemuth et al., 2005; Presswood et al., 2008; Reiman et al., 2009; Souza et al., 2009). Individual running techniques may demonstrate combinations of the adaptations below but clearly not simultaneous medial and lateral knee drift. Further, the gait adaptations may also occur during walking visualized as a waddling motion or a limp.
Table 1 shows gait adaptations due to a weak gluteus medius muscle during running.
Gait adaptationsAreas at risk of structural overloadTrendelenburg gaitLumbar spine, sacroiliac joint (SIJ), greatertrochanter bursa, insertion of muscle ongreater trochanter, overactivity of piriformisand tensor fascia lata (TFL)Medial knee driftLateral tibiofemoral compartment (via(valgus position ofcompression), patellofemoral joint, patellatibiofemoral joint)tendon and fat pad, pes anserinus, iliotibialband (ITB), anterior cruciate ligament strain(ACL)Lateral knee driftMedial tibiofemoral compartment (via(varus position ofcompression), ITB, posterolateral knee softtibiofemoral joint)tissues (via tension), popliteusSame sided shift of trunkLumbar spine (increased disc and facet joint(lateral flexion of trunk)compression), SIJ (increased shear)
The most commonly diagnosed lower limb soft tissue injuries caused by distance running are iliotibial band syndrome, tibial stress syndrome, patellofemoral pain syndrome, Achilles tendonitis and plantar fasciitis (Yeung & Yeung 2001). From the table above, a common adaptation from weakness of the gluteus medius muscle during the stance phase of running occurs when the femur excessively adducts or internally rotates. These motions increases the tension on the iliotibial band (Taunton et al., 2002) and cause abnormal patellofemoral contact stress (Souza & Powers, 2009). Continuing down the kinetic chain, internal rotation of the femur also allows the knee to fall into a valgus position and promotes the tibia to rotate internally relative to the foot and increases the weight transfer to the medial aspect of the foot. These motions increase the risk of any condition relating to excessive and/or prolonged pronation of the foot such as tibial stress syndrome and Achilles tendonitis (Lundberg et al., 1989). Further, the combination motions of ankle pronation and knee valgus are implicated as the primary mechanism of non-contact ACL injury in sports where running is an integral component (Souza & Powers, 2009).
In addition, poor lumbo-pelvic posture due to abnormal sagittal plane or frontal plane pelvic rotations leads to compensation in the thoracic spinal posture and subsequent shoulder dyskinesis (Borstad, 2006; Greenfield et al., 1995). Poor thoracic posture relates to an increased forward curve of the thoracic region of the spine (kyphosis) and produces a ‘hunching’ or ‘hump back’ appearance and a rounding of the shoulders. The rounding of the upper back and shoulders cause the head and neck to tilt downward thus to look straight ahead requires the head to be lifted upward and forward. This forward head posture causes several clinical symptoms and also the continuation of many clinical issues including headaches, pain between the shoulder blades, upper back pain, neck pain, numbness and tingling of the fingers and shoulder pain. Pain originating from the shoulder could also radiate into the neck, head, arm, or chest.
Respiratory dysfunction is also caused from an excessive rounding of the shoulders which is a sequence of abnormal kinematic events of the scapula, clavicle and humerus. First, thoracic kyphosis causes abnormal three-dimensional scapular kinematics including scapular protraction, downward rotation and anterior tilting. The humerus articulates with the scapula at the glenohumeral joint and abnormal scapular kinematics causes the humerus to shift down and rotate inwards toward the center of the body. The scapula also articulates with the clavicle at the acromioclavicular joint hence abnormal scapular and humeral kinematics causes abnormal clavicular kinematics, namely clavicular protraction, and increases force transmission of the proximal portion of the clavicle on the first rib at the sternoclavicular joint. The increased force transmission at this joint in combination with thoracic kyphosis limits the ability of the ribs to expand during respiration and the respiratory muscles to properly function thus reducing lung volume and blood oxygenation.
Collectively, core strength imbalances stemming from weakness of the gluteus medius muscle may be associated with or predispose an individual to injury. Successful preventative strategies for the knee during running include modifying training schedules or external body support (i.e., patellar knee brace, footwear, lumbar brace) (Yeung & Yeung, 2009). However, it has been shown that gluteus medius muscle strengthening exercises reduces the magnitude of frontal plane pelvic drop (Presswood et al., 2008), improves performance (Lephart et al., 2007) and reduces clinical symptoms in the soft tissues of the hip (Bolgla & Uhl, 2005), knee (Boling, Bolgla, Mattacola, Uhl, & Hosey, 2006; Mascal, Landel, & Powers, 2003; Nakagawa et al., 2008) and lumbar area (Nelson-Wong, Gregory, Winter, & Callaghan, 2008). Further, strength and kinematic improvements in the lumbar area are related to improvements in the thoracic area and leads to beneficial changes in shoulder and respiratory function.
Various braces are known that can mitigate some of the above challenges. However, braces tend to be uncomfortable, heavy, and aesthetically displeasing, especially when worn for long periods of time (e.g., a full day on the ski slopes). As a result, braces are often not worn for as long as they could be and thus their beneficial effects are not fully felt. Further, braces are used to immobilize or compensate for a change in joint stability or angular position caused by muscular weakness or injury and are thought to promote atrophy of the muscles surrounding the joint leading to secondary clinical problems. There is therefore a need in the art for physiological support mechanisms that are lightweight, comfortable, and fashionable and that facilitate functional movement and muscular function of the kinetic chain.